The present invention relates generally to endless conveyors for aggregate materials and, more particularly, to a conveyor pan assembly for an armored face conveyor for handling coal in a longwall mining system.
Various types of conveyor pan assemblies for armored face conveyors are well known in the art. Typically, each pan assembly includes a deck plate positioned between and providing support for a pair of parallel sidewalls. The deck plate provides a conveying surface for the coal or other aggregate material being conveyed. The sidewalls form tracks for the longwall mining machine as it moves back and forth along the mine face.
Attachment of the sidewalls to the deck plate is attained by placing elongated structural welds along the upper and lower chamfered lateral edges of the deck plate. Usually, the sidewalls are cast in a sigma shape such that when the deck plate is placed between them, upper and lower troughs or runs are defined. Of course, the upper trough of each pan assembly serves to guide the flight bars pulled along by a drive chain for moving the aggregate material along the conveyor line to a takeaway conveyor; the inverted lower trough guiding the flights during the return. To form the conveyor line, a plurality of the pan assemblies are placed in an end to end relationship, usually by forming a welded joint between specially shaped mating faces on the ends.
One prevalent problem with known types of conveyor pan assemblies is that the structural welds between the deck plate and the sigma sidewalls are positioned both above and below the conveying surface, as shown in Westfalia""s U.S. Pat. No. 4,484,677 to Berwald. There are several shortcomings in this design. The first is that placing two full length structural welds along the entire length of both lateral edges above and below the deck plate greatly increases the manufacturing time and expense. The second is that these above (or top) structural welds along the sidewalls are thus exposed to significant wear created by the flights and aggregate material moving over them along the upper run of the conveyor line. This deleterious wear on these critical structural welds is the single most important factor limiting the service life of the conveyor pan assembly. Forming the deck plate of hardened steel or other abrasion-resistant materials reduces wear on the conveying surface, but the structural welds holding the deck plate in place are softer and wear more quickly. If the structural welds on the deck plate holding the sidewalls in place are significantly weakened, the support of the mining machine is threatened. Deleterious production downtime is required while the mining operation is temporarily shut down to remove and repair the pan assembly, including replacing the deck plate. The complete failure of one of these structural welds can even lead to a total failure of the longwall mining and armored face conveyor system if the developing weakness is not detected in time.
A number of solutions have been proposed to eliminate the deleterious effects of wear on the structural welds created by the flights and aggregate material, as well as to reduce the amount of structural welding required to provide a strong, long-lasting conveyor pan assembly. One recent proposal is found in U.S. Pat. No. 5,131,724 to Bandy, Jr. et al., of which I am a co-inventor. A deck plate with outwardly projecting keys fit into mating slots formed in the sigma sidewalls. By placing the structural welds exteriorly of the sidewalls where the keys project through the slots (see FIG. 2 of the ""724 patent), the deleterious effects of wear created by the flights/aggregate material are eliminated.
While this pan assembly overcomes the wear problem and is a significant improvement over prior art proposals, one remaining limitation is that the upper deck plate is still attached directly to and provides the sole support for the sigma sidewalls. Thus, when the deck plate eventually wears out and is in need of replacement, the entire pan assembly must disassembled. This includes: (1) cutting the structural welds formed around the keys on the lateral edges of the deck plate where they project through the slots in the sigma sidewalls; (2) removing the worn deck plate; (3) making the necessary repairs; and (4) reinstalling a replacement deck plate. To do this, the sidewalls must be physically removed and separated apart from the deck plate. The spacing between the sidewalls is no longer set. The next step (5) thus involves the difficult and tedious step of realigning the sidewalls and resetting the spacing to receive the deck plate. Finally, step (6) involves proceeding to weld the deck plate back in place between the opposed sidewalls. This has thus proven to be a very time consuming and labor intensive operation.
While there have been improvements in this basic technology such as is found in the conveyor pan assembly shown and described in U.S. Pat. No. 5,871,261, of which I am also a co-inventor, these changes are directed to other features. For example, in this ""261 patent, elongated bevels are added along the entire lower longitudinal edges of the deck plate to mate with similar bevels on the sidewalls. But, with this change in the structure, the same basic repair/replacement procedure as in the ""724 patent is required.
To try to facilitate this repair of the pan assembly, including replacement of the deck plate, without disconnecting the sidewalls, others have proposed splitting the conveyor pan assemblies, including the sigma sidewalls, into separate upper and lower sub-assemblies that are mechanically fastened together by a connector bar. An example is found in Westfalia""s U.S. Pat. No. 4,632,239 to Schoop et al., wherein external connector bars and fastener assemblies are used to secure the two sub assemblies together. While this arrangement permits removal of the upper sub-assembly with the deck plate for replacement, without the need for cutting structural welds, a different problem appears. These extra components are expensive and the fasteners are sometimes difficult to loosen for replacement due to the build-up of rust, corrosion and other debris. Furthermore, any kind of mechanical connection such as this, can over time loosen on its own due to the vibration of the mining machinery. Specifically, the connector bars/fasteners may loosen due to the significant jarring caused by the traversing mining machine supported on the sidewalls. Furthermore, loosening action can be aggravated by the vibrations created as the flights and aggregate materials move along the conveyor. Of course, even a slight misalignment of the upper sidewall section and the deck plate during the replacement effort, can make it difficult to reapply and tighten the connector bars/fasteners. Even when the sigma sidewalls are made integral, the connector bars/fasteners are required, and the full length side welds must be cut in order to replace the deck plate.
Thus, a need is identified for an improved conveyor pan assembly having a deck plate that is easier to install and remove, and is more economical in both initial cost and maintenance. The sigma sidewalls would remain assembled with a support plate so that the spacing is always maintained. All structural welds for holding the deck plate in place would be positioned away from the conveying surface. As an added advantage, the amount of structural welding required during fabrication of the conveyor pan assembly would be reduced without compromising its structural strength. Mounting the deck plate, but not the support plate, in an offset position in a longitudinal direction would also facilitate forming a secure overlapping joint with the next-in-line conveyor pan assembly. There would be no need for specially forming the ends of adjacent conveyor pans to fit together. Overall, the conveyor pan assembly would result in a significant improvement over prior art proposals, particularly in terms of ease and cost of manufacturing, service life, reliability, and structural integrity.
Keeping the foregoing needs in specific focus, it is a primary object of the present invention to provide a conveyor pan assembly that overcomes the limitations and shortcomings of the above-referenced prior art conveyor pan assemblies.
Another object of the present invention is to provide a conveyor pan assembly including an easily replaceable deck plate that forms a conveying surface and a lower support plate extending between and spacing the opposed sidewalls, whereby during installation or removal of the upper deck plate for replacement, the sidewalls remain attached to and fully supported by the lower support plate.
Still another object of the present invention is to provide a conveyor pan assembly in which each lateral edge of a deck plate can slide along corresponding grooves formed in a pair of opposed sidewalls to facilitate installation or removal of the deck plate, while the lower support plate remains in position between and fully maintains the spacing of the sidewalls.
A related object is to provide a conveyor pan assembly in which lateral edges are captured and held by a tongue and groove joint that allows the deck plate to be easily slid into and out of position to form the pan assembly.
Another object is to provide such a pan assembly wherein one end of the deck plate is offset relative to the sidewalls and the support plate to form an overlapping joint with the next-in-line pan assembly, thereby avoiding the need for specially forming the ends of the support plate.
A further object of the present invention is to provide the lower support plate in a conveyor pan assembly with at least one slot for receiving a structural weld that assists in holding the upper deck plate in position relative to the sidewalls of the pan assembly, whereby placing the weld in the slot and away from the conveying surface, where it would otherwise be subject to the deleterious effects of wear created by the flights moving the coal or other aggregate material along the feed path.
Yet another object of the present invention is to provide a conveyor pan assembly wherein the support plate is further welded along only its lateral edges to a plurality of spaced tabs projecting inwardly from each sidewall, whereby the overall amount of structural welding required during fabrication of the conveyor pan assembly is further significantly reduced.
Still a further object of the present invention is to provide a method of fabricating a conveyor pan assembly wherein the deck plate is easily installed or removed for replacement; and also a method is provided for more efficiently forming a conveyor line from a plurality of such pan assemblies.
Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, an improved conveyor pan assembly is disclosed for an armored face conveyor system, such as for handling coal or other aggregate material. Each conveyor pan assembly includes: (1) a lower support plate attached to and extending between a pair of opposed sidewalls; and (2) an upper deck plate placed over the lower support plate to provide the conveying surface. As outlined above, and as will be seen in further detail from the discussion which follows, providing separate deck and support plates in accordance with the present invention provides several significant advantages in forming the conveyor pan assembly of the present invention.
In accordance with the first of several important aspects of the invention, each lateral edge of the upper deck plate forms a full length tongue that is received in a corresponding elongated groove formed in the adjacent sidewall. Advantageously, the lateral side edges can slide along the grooves to simplify installation or removal of the deck plate, while the sidewalls remain attached to and supported upright and properly spaced by the lower support plate. There is no need for disconnecting the sidewalls from the lower support plate. As should be appreciated, this sliding tongue and groove joint significantly eases the process of installation of the upper deck plate during manufacturing. Also, when the upper deck plate becomes worn and is in need of replacement, the tongue and groove joint also facilitates removal of the deck plate.
In the preferred embodiment, the sidewalls are sigma-shaped in cross section and formed of cast steel to provide superior strength to the pan assembly. The support plate is mild rolled steel, while the deck plate is hardened, abrasion resistive steel.
The deck plate in combination with the adjacent upper recesses or indentations in the sigma sidewalls define an upper run portion for guiding the flights and confining the coal as the flights are being driven by a drive chain along the feed path. Below the support plate, a similarly configured, but inverted lower run portion is provided for guiding the flights during the return trip to form the endless conveyor.
Each sigma sidewall preferably includes a plurality of spaced, inwardly projecting tabs that serve as attachment points for the lateral edges of the support plate. In addition to providing an attachment point, each tab also serves to define inwardly projecting extensions of the lower edge of the groove formed in each sigma sidewall. In forming the preferred pan assembly of the present invention, the lateral edges of the support plate are structurally butt welded to each tab. The tabs, as well as the structural welds holding the support plate in place to the sidewalls, are advantageously protected from wear.
As should be appreciated, the use of spaced tabs for receiving the structural welds to hold the lower support plate in place avoids the need for welding along the entire length of the pan assembly. This advantageously reduces the manufacturing effort and expense. Although fewer structural welds are required, the strength of the fully assembled pan assembly is not compromised. This is because additional structural support is provided by the tongue and groove captivation joint formed between the deck plate and the sidewalls. In other words, this overlapping support serves to transfer the weight of the coal or other aggregate material being conveyed over the entire length of the lateral tongue and groove joints defined by the tabs and over the support deck welded thereto.
In accordance with another important aspect of the invention, the support plate includes at least one slot extending therethrough for receiving at least one structural weld. This structural weld further assists in holding the upper deck plate in place between the sigma sidewalls. By placing this structural weld in a slot totally away from the conveying surface, the potential for wear to the weld, as created by the flights moving along the feed path of the armored face conveyor, is also eliminated. The weld is preferably focused at the interface between the upper edge of the slot and the exposed underside surface of the upper deck plate. Preferably, several slots and welds are used. Depending on the number of these welds used, each need extend over only a relatively small surface area, and to a minimum depth. For example, in some relatively light duty pan assemblies, tack welds can be used. In other situations, a bead weld can fully fill the slot for maximum strength.
Thus, as should now be appreciated, all of the structural welds holding the upper deck plate in place, as well as the welds attaching the lower support plate to the sidewalls, do not form any part of the conveying surface and thus are not exposed to wear. This advantageously extends the service life of the conveyor pan assembly considerably, which in turn reduces the maintenance and repair expense. Additionally, significant periods of costly production downtime due to potential mining machine and conveyor shutdowns are eliminated. Also, the replaceable upper deck concept of this invention allows each pan assembly to be repaired and placed back into production in the shortest possible time.
The upper deck plate in the conveyor pan assembly of the preferred embodiment is mounted in an offset position in a longitudinal direction relative to the lower support plate. In this offset position, one end of the upper deck plate can form an overlapping joint with the next-in-line conveyor pan assembly. The extended lip of the deck plate mates with an exposed narrow strip of the support plate on an adjacent pan assembly to form the joint. This feature avoids the need for specially machining or otherwise forming the ends of the conveyor pan assemblies to mate together to form a conveyor line, as is typical of many known types of pan assemblies. This reduces manufacturing expense and also provides flexibility in swapping conveyor pan assemblies between different conveyor lines formed of similar types of pan assemblies. The overlapping joint eliminates interference with the flight bars as they are pulled along the feed path defined by the deck plate.
In accordance with another important aspect of the present invention, a method of fabricating a conveyor pan assembly, as well as a conveyor line made up of the pan assemblies, is disclosed. The method includes the step of attaching a lower support plate to a pair of opposed sidewalls, such as by welding it in place to inwardly projecting edges on the sidewalls. Preferably, these sidewall edges are formed as spaced tabs. Each of the sidewalls is thus provided with a lateral groove for receiving the lateral edges of an upper deck plate to form tongue and groove joints along the sides. Advantageously, to form these joints, the upper deck plate is simply slid into position as it is held in the grooves. The upper deck plate is then simply attached to the lower support plate to assist in holding it in place, such as by placing welds in slots formed in the lower support plate, or other equivalent attachment means.
The method may also include the step of mounting the upper deck plate in an offset position in a longitudinal direction relative to the lower support plate and the sidewalls, such that an overlapping joint may be formed with a next-in-line conveyor pan. It should also be recognized that during manufacturing, the ability of the upper deck plate to slide along the tongue and groove joint formed between the sidewalls greatly facilitates mounting it in this offset position. By interfitting a plurality of pan assemblies manufactured in accordance with the foregoing description, the continuous conveyor line for the armored face conveyor is provided.
Still other objects of the present invention will become apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of this invention, simply by way of illustration of one of the modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.